The influence of indenter tip rounding on the indentation size effect

A model was developed to interpret the indentation size effect. The model considers the tip wear effect, causing a rounded tip, the plastic zone size and various strengthening contributions, including geometrically necessary dislocations, preexisting statistically stored dislocations and grain size. It is shown that the shape of the worn tip can be effectively determined through calibration experiments. The model is applied to predict dislocation densities, and shows a good correspondence with published data on dislocation densities in copper single crystals. Predicted ISE is shown to be in good correspondence with published data on a range of metals, and an improvement over existing models is demonstrated

Microembossing of ultrafine grained Al: microstructural analysis and finite element modelling

Ultra fine grained (UFG) Al-1050 processed by equal channel angular pressing (ECAP) and UFG Al-Mg-Cu-Mn processed by high pressure torsion (HPT) were embossed at both room temperature and 300 °C, with the aim of producing micro-channels. The behaviour of Al alloys during the embossing process was analysed using finite element (FE) modelling. The cold embossing of both Al alloys is characterised by a partial pattern transfer, a large embossing force, channels with oblique sidewalls and a large failure rate of the mould. The hot embossing is characterised by straight channel sidewalls, fully transferred patterns and reduced loads which decrease the failure rate of the mould. Hot embossing of UFG Al-Mg-Cu-Mn produced by HPT shows a potential of fabrication of microelectromechanical system (MEMS) components with micro channels

Al-Mg-Cu based alloys and pure Al processed by high pressure torsion: the influence of alloying additions on strengthening

The influence of alloying additions on strengthening on high pressure torsion (HPT) processed alloys was investigated using commercially pure Al (Al-1050 alloy) and five Al-(1-3)Mg-(0-4)Cu alloys (in wt%). Microhardness was measured on cross sections. For Al-1050 the microhardness reaches a peak at an effective strain of about 3 and subsequently decreases. The microhardness of Al-Mg-Cu alloys increases strongly and continuously with increasing equivalent strain. This workhardening rate is enhanced by increasing Mg content over the entire range of strain. Furthermore, the workhardening rates were higher in Cu-free and low Cu-containing (? 0.4%) Al-Mg alloys as compared to high Cu-containing Al-Mg alloy at strains less than 3. A model is presented that describes the experimental results well. The strengthening model indicates that dislocation-solute and dislocation-cluster interactions play an important role

Morphology control via dual solvent crystallization for high-mobility functionalized pentacene-blend thin film transistors

We present an approach to improving the performance of solution processed organic semiconductor transistors based on a dual solvent system. We here apply this to a blend containing the ?-conjugated small molecule 6,13 bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) and polystyrene, which acts as an inert binder. Using a semiconductor-binder solution of two solvents, where the main solvent is a better solvent of the small molecule and second solvent is a better solvent of the polymer, crystal morphologies can be altered and transistor mobilities increased by almost an order of magnitude. In this way, air-ambient and solution-processed transistors with linear and saturation mobilities higher than 1 cm2 V?1 s?1 have been fabricated. We discuss how the solubility properties of the formulation components can be used to identify solvent candidates that promote an efficient self-assembly of the small molecule

Using differential scanning calorimetry as an analytical tool for ultrafine-grained metals processed by severe plastic deformation

Differential Scanning Calorimetry (DSC) is a thermal analysis technique that measures the energy absorbed or released by a sample as a function of temperature or time. Analysis by DSC has wide applications for examining solid-state reactions and solid-liquid reactions in many different materials. Quantitative analyses of the kinetics of reactions may be assessed by reviewing the interrelation between activation energy analysis methods. In recent years, DSC has been applied in the examination and analysis of bulk ultrafine-grained materials processed through the application of Severe Plastic Deformation (SPD). This overview examines these recent reports with reference to materials processed using the procedures of Equal-Channel Angular Pressing (ECAP), High-Pressure Torsion (HPT) and Accumulative Roll-Bonding (ARB). In addition, some critical issues related to DSC analysis are also discussed

Strengthening of an Al-Cu-Mg alloy processed by high-pressure torsion due to clusters, defects and defect-cluster complexes

A physically-based model is established to predict the strength of cluster strengthened ultrafine-grained ternary alloys processed by severe plastic deformation. The model incorporates strengthening due to dislocations, grain refinement, co-clusters (due to short range order and modulus strengthening) and solute segregation. The model is applied to predict strengthening in an Al-Cu-Mg alloy processed by high-pressure torsion (HPT). The microstructure was investigated using transmission electron microscopy (TEM), atom probe tomography (APT), and X-ray diffraction (XRD). Analysis of XRD line profile broadening shows that the dislocation density increases significantly due to severe plastic deformation, which contributes to the increase of strength. APT reveals the presence of nanoscale co-clusters and defect-solute clustering. The concepts of the multiple local interaction energies between solutes and dislocations were used to quantitatively explain the strengthening mechanisms. The model shows a good correspondence with measured microstructure data and measured strength

Grain structure and texture development during ECAP of two heat-treatable Al-based alloys

The microstructures of a spray-cast Al-7034 (Al-Zn-Mg-Cu) alloy and an Al-2024 (Al-Cu-Mg) alloy were studied using electron back-scatter diffraction (EBSD) after processing through equal-channel angular pressing (ECAP). The EBSD results demonstrate there is a relatively rapid increase in the fraction of low-angle boundaries during the initial ECAP passes and a subsequent more gradual increase in the fraction of high-angle grain boundaries in subsequent passes. The crystallographic textures and their rotations during ECAP were analysed through EBSD